Slab Leaks: Signs, Detection and Repair Costs

A slab leak is a leak in a water supply or drain pipe that runs in or under a home's concrete slab foundation. The common signs are a water bill that jumps for no reason, a water meter that keeps moving when everything is off, warm spots on the floor, the sound of running water, and damp or damaged flooring. It is found with a simple meter test and then pinpointed by a plumber with leak detection equipment, and it is repaired by opening the slab at the leak, rerouting the line, or lining the pipe.

What is a slab leak?

Many homes are built on a concrete slab poured directly on the ground. The water supply lines, and often the drain lines, run through or beneath that slab. When one of those pipes develops a leak, the water has nowhere visible to go. It soaks into the soil and can come up through the concrete into flooring, walls and cabinets.

There are two kinds:

Hot water line leaks are often noticed first because they warm the floor and keep the water heater running.

Slab leak signs to watch for

• A higher water bill with no change in how you use water
• The water meter moving when every faucet, toilet and appliance is off
• Warm or hot spots on tile or concrete, often noticed barefoot or by pets lying there
• The sound of running water when nothing is on
• Damp or wet flooring, carpet that's wet with no spill, or cupped wood or swollen laminate
• Mold or a musty smell near the floor or baseboards
• Low water pressure or a water heater that runs more than usual
• Cracks in walls or floors, or water pooling outside near the foundation

Several of these overlap with other leaks. Our guide to signs of water damage covers what each one usually means.

How to find a slab leak: the meter test

You can check for a hidden leak yourself before calling anyone. The EPA's WaterSense program recommends taking two meter readings two hours apart with no water running; if the meter changes at all, you probably have a leak.

1. Turn off every faucet, shower, toilet fill, dishwasher, washer, ice maker and irrigation system.
2. Find your water meter (usually near the street in a ground box) and note the reading or watch the small leak indicator dial.
3. Wait two hours without using any water.
4. Check the meter again. Any movement points to a leak.
5. Next, close the main shutoff valve at the house. If the meter still moves, the leak is between the meter and the house. If it stops, the leak is inside the house, which includes lines under the slab.

A meter test doesn't tell you the leak is under the slab. A running toilet is a very common cause, so check toilets first. The EPA also suggests a winter check: a family of four using more than 12,000 gallons per month may have serious leaks.

How slab leaks happen

Plumbers commonly point to a handful of causes:

• Corrosion of metal pipes, especially older copper or galvanized lines, sometimes made worse by water chemistry
• Abrasion, where a pipe expands and contracts against concrete, gravel or another pipe until it wears through
• Poor installation, such as kinked or damaged pipe, or fittings buried in the slab
• Soil movement, from expansive clay, settling or earthquakes, putting stress on pipes
• High water pressure over many years

Age is a factor in all of these. If one slab leak has happened in an older home, the rest of the original piping is the same age and material.

Slab leak detection: how a plumber pinpoints it

Once a leak is confirmed, a leak detection specialist narrows it down without breaking concrete everywhere. Common methods:

Fixr's cost guide (updated May 2025) says leak detection itself costs from $100 to $400, depending on how invasive the search is.

How to fix a slab leak: repair options

Which one makes sense depends on where the leak is, the age and material of your pipes, whether it's a first or repeat leak, and what's on the floor above. Ask for written options from more than one licensed plumber.

Slab leak repair cost

The main cost drivers are:

• Detection and how hard the leak is to locate
• Repair method: spot repair versus reroute versus repipe
• Flooring above the leak: tile, hardwood and stone are expensive to remove and match
• Water damage cleanup: drying the slab, replacing wet drywall, baseboards, cabinets or flooring
• Mold, if the leak went on for a long time
• Permits and concrete patching

Fixr's slab leak cost guide (updated May 2025) gives a national average of $2,500, with most jobs between $1,000 and $4,000. By method, Fixr lists breaking the slab at $500 to $3,000, pipe lining at $500 to $2,000, tunneling at $900 to $2,000, and rerouting at $4,000 to $15,000. Those figures are for the plumbing work; water damage repair to floors and walls is extra. Restoration work is priced separately.

Slab leak in the garage

A garage slab leak usually shows up as a damp patch or crack that stays wet on the garage floor, sometimes with efflorescence (white mineral deposits) on the concrete. It can come from a supply line running under the garage to the house or to a hose bib, or from water coming in from outside. The meter test is the same. Garage leaks are often easier to access because there is no finished flooring to remove.

Water damage after a slab leak

The leak repair stops new water. It does not dry what's already wet, which is the job of water damage restoration. Slab leaks often soak:

• Carpet and pad, see wet carpet after water damage
• Wood and laminate floors, see water-damaged wood floors
• Drywall and baseboards, see water-damaged drywall
• Cabinets and the concrete itself

The EPA advises drying water-damaged areas and items within 24 to 48 hours to prevent mold growth. With a slab leak, the area has often been wet much longer before anyone noticed, so check for mold under flooring and behind baseboards. Concrete dries slowly; the EPA's cleanup table recommends removing water with extraction equipment and then using dehumidifiers, fans or heaters to speed drying of concrete. A water damage restoration company can measure moisture in the slab and set up drying.

Will insurance cover a leak under a slab?

Often partly. Policies differ, but the standard ISO HO-3 sample policy published by the Insurance Information Institute covers water damage from a plumbing system and includes the cost to tear out and replace any part of a building, but only when necessary to repair the system. The same form says it does not cover the system or appliance the water escaped from, which means the pipe repair itself is often not covered while the resulting water damage and access may be.

The Insurance Information Institute also says seepage is viewed as a maintenance issue and is not covered, so a leak that went on for a long time can be treated differently from a sudden one. Some insurers sell endorsements specifically for slab leaks or service lines. Read your policy, call your agent, and document everything. Our water damage insurance claims guide walks through the process.

Is a slab leak an emergency?

A slab leak is not usually an emergency in the same way as a burst pipe flooding a room, but it should be handled within days, not months. Water running under a foundation wastes water, damages flooring and can affect the soil under the slab. If water is actively coming up through the floor, shut off the main valve and call a plumber. Renters should report it to the landlord or property manager in writing right away, since repairs to building plumbing are usually the owner's responsibility under the lease; renters insurance generally covers belongings, not the building.

If water has already damaged floors or walls, local restoration companies can help dry and repair them. Browse our locations to find help nearby.

Flood Rescue Pros is a free service that connects homeowners with independent local water damage restoration companies. Get help now.

Frequently asked questions

How do slab leaks happen?

Most come from pipe corrosion, pipes rubbing against concrete or gravel as they expand and contract, installation damage, soil movement under the slab, or long-term high water pressure. Older pipes are more prone to all of these.

How do I find a water leak that is not visible?

Do a meter test: turn off all water, read the meter, wait two hours, and read it again. The EPA says any change probably means a leak. A plumber can then locate it with pressure testing, acoustic equipment or thermal imaging.

What does a slab leak cost to fix?

Fixr's May 2025 guide gives a national average of $2,500, with most jobs between $1,000 and $4,000, and rerouting all lines from under the slab at up to $15,000. Water damage repair to flooring is extra.

Will insurance cover a leak under a slab?

Many homeowners policies cover the water damage and the cost of tearing out the floor to reach the pipe, but not the pipe repair itself. Long-term seepage may be excluded. Check your own policy.

Can you live in a house with a slab leak?

Usually, for a short time, but get it repaired soon. Shut off the water if it is coming up through the floor, and watch for mold, wet flooring and electrical hazards near the water.

What are the first signs of a slab leak?

A water bill that rises for no reason, a meter that moves when all water is off, warm spots on the floor, and the sound of running water are common early signs.

Key facts

• A slab leak is a leaking water or drain line in or under a concrete slab foundation.
• Check for one with the EPA's meter test: no water use for two hours; any meter movement probably means a leak.
• Detection uses pressure testing, acoustic listening, thermal imaging or tracer gas; Fixr lists detection at $100 to $400.
• Repairs include spot repair through the slab, rerouting, repiping or pipe lining; Fixr's national average is $2,500.
• Homeowners policies often cover resulting water damage and tear-out, but not the failed pipe itself.
• Dry wet flooring and walls quickly after the repair; the EPA advises drying within 24 to 48 hours to prevent mold.